1. Field of the Invention
The present invention relates to a method for producing a diol or triol, which method comprises a step of removing impurities from a diol- or triol-containing solution.
2. Description of the Related Art
Diols and triols are compounds which are industrially very important as raw materials of polymers and as raw materials of pharmaceutical agents. Diols such as butanediol and ethylene glycol produce polyesters when they are copolymerized with dicarboxylic acids such as terephthalic acid and adipic acid. Further, glycerin, which is a trial, is used as a raw material of cosmetics and the like. It is well known that these dials and triols can be produced by chemical synthesis, but, in recent years, since they can be produced by biochemical methods such as fermentation methods and enzymatic methods, they are drawing attention as nonpetroleum biopolymer materials. Therefore, technologies by which such dials and triols can be produced at high purity and at high efficiency have been demanded.
In general, as the method for purifying dials and trials, solvent extraction or distillation is employed. In solvent extraction, in cases where the desired product is a lower alcohol, which is highly soluble in water, distribution of the lower alcohol into the organic phase is difficult, so that use of a special extraction solvent or multistep extraction may be required, leading to increase in the cost (Patent Document 1). Further, in purification by distillation, if impurities are contained, distillation residues are generated, leading to decrease in the yield. Further, diol- and triol-containing liquids prepared by the fermentation method contain sugars, which are nutrient sources of microorganisms, and organic acids and proteins, which are metabolites, and these are reported to yield colored impurities by heating (Non-patent Document 1). Therefore, in order to carry out purification of highly pure dial or triol and highly efficient production thereof, removal of impurities in the fermentation broth is very important.
As methods for producing highly pure diol or triol, a method for producing 1,3-propanediol wherein distillation purification is carried out in combination with microfiltration, ultrafiltration, nanofiltration or ion exchange (Patent Document 2); and a method for separating diol using a reverse osmosis membrane or a nanofiltration membrane (Patent Document 3) are disclosed. However, they do not disclose the effect of difference in the material of the nanofiltration membrane on the permeation selectivity and on purity of the diol or triol after the purification.